This invention relates to an apparatus for recovering valuable metals from solid scrap mixed non-magnetic metals and non-metallic materials, and more particularly to a separating apparatus using eddy currents, which apparatus is equipped with a device for rolling non-magnetic metal pieces and a device for screening these metal pieces according to sizes.
For recovery of metals from crushed metal pieces or ore pieces, there is known a method for recovering metals according to the magnetic susceptibility of such metals, i.e. by means of a magnetic separator utilizing a magnetic attracting force of such a metal. On the other hand, separation of metals having low susceptibility, or non-magnetic metals, such as copper, aluminum and zinc, has been practiced manually. With a view to automating the recovery of non-magnetic metal pieces, an attempt has been proposed for crushing such non-magnetic metal pieces into fine pieces and separating for recovery fine pieces of nonmagnetic metals according to an electromagnetic technique. More in detail, a method has been proposed in which an abrupt change in magnetic fields is applied to a mixture of non-magnetic metal pieces and non-metallic pieces, so as to induce eddy currents in the metal pieces only, and separation of non-magnetic metal pieces from non-metallic pieces is carried out by the interaction between a magnetic field induced by the eddy currents and an external magnetic field. The principle of such a method is disclosed, for example, in the U.S. Pat. No. 3,448,857. The separating capability of an apparatus disclosed therein is largely dependent upon the shape, size and density of crushed pieces being separated. Particularly, the shape of metal pieces should preferably be flat for increasing the quantity of magnetic flux permeating therethrough. With the prior art apparatus for use in separation and recovery of non-magnetic metal pieces, however, it has been customary to charge the apparatus with crushed pieces of a randum shape and varying sizes, so that eddy currents have found difficulty in flowing through fine, lump-like crushed pieces. Accordingly, a strong magnetic field and high field frequency have been required. This has offered a difficulty in the manufacture of the separating apparatus as well as presented disadvantages from the viewpoint of accuracy in separation. Another problem has been encountered with the case where crushed pieces of a randum shape and varying sizes are processed at a time in the aforesaid separating apparatus, i.e., crushed pieces of a large size tend to wrap small-sized pieces therein, leading to the lowered separating accuracy of the apparatus. Furthermore, due to the fact that the metal pieces having high electric conductivity, such as aluminum and copper, are separable more easily than the other, it is imperative that a magnetically improved separating condition be provided for pieces of other metals, such as tin, zinc, lead, their alloys and stainless steels.